The present invention is directed to protection of a power converter device during operation, and especially to protecting a power converter device against damage that may be caused by an excessive current condition.
One common implementation of a current protection scheme is a peak current limiter that prevents the maximum peak current from the power converter from exceeding a threshold peak current value. Peak current protection schemes are particularly useful in applications of power switching mode power converters because of the fast response by such schemes to over-current conditions and simple implementation of such schemes. A peak current control device works well when the duty cycle of the power converter is less than fifty percent. However, when the duty cycle of the power converter is greater than fifty percent, the peak current control device is not stable and exhibits a sub-harmonic oscillation. Another limitation of peak current control devices is sensitivity to switching noise. Designs of such peak current control devices must take into account such sensitivity to switching noise to avoid false alarms that may be caused by spurious noise injections. In applications where a precise maximum load current is desired, peak current control is unacceptable due to large variations in average load current as duty cycle varies.
There is a need for a current limit control apparatus and method for use with a power converter device that is substantially stable and exhibits little or no sub-harmonic oscillation.
There is a need for a current limit control apparatus and method for use with a power converter device that is substantially immune to noise.
There is also a need for a current limit control apparatus and method that can limit average load current in a manner that is substantially independent of duty cycle variations which may be caused by line voltage or load resistance.